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The pathophysiology of femoroacetabular impingement (FAI) remains to be better understood, including factors affecting symptom development and disease progression.(1) To determine rates of initial and subsequent symptom development in the contralateral hip of patients with symptomatic FAI and (2) to identify predictors of the development of symptomatic contralateral FAI.Case-control study; Level of evidence, 3.This prospective study cohort included the contralateral hip of 179 consecutive patients undergoing primary surgical treatment of FAI. At presentation and follow-up time points, patients recorded the presence of symptoms in the contralateral hip. Patients with a minimum 1-year follow-up were included in the final cohort. Univariate analysis compared the patient characteristics and FAI imaging characteristics (cam and pincer) of initially asymptomatic patients who developed symptoms and those who remained asymptomatic. Kaplan-Meier survival curves were calculated to demonstrate symptom development over time.A total of 148 patients (83%) were followed for at least 1 year (mean, 2.9 years). Thirty-four (23%) patients had symptoms in the contralateral hip at the time of the initial presentation. An additional 27 hips (24% of the initially asymptomatic) developed symptoms during the follow-up period at a mean 2.0 years from presentation. Head-neck offset ratio on the anteroposterior pelvis radiograph was significantly lower among hips that developed symptoms (0.153 vs 0.163 asymptomatic group, P = .027). Maximum alpha angle (P = .503), lateral center edge angle (P = .975), and crossover sign (P = .865) were not predictive of the development of symptoms. Patients developing contralateral hip symptoms were less likely to have a UCLA (University of California, Los Angeles) activity score of 9 or 10 at presentation (18.2% vs 43.8%, P = .032). The total arc of rotation in flexion (internal rotation in 90° of flexion + external rotation in flexion) was significantly decreased in hips developing symptoms (39.4º vs 50.4º, P = .012). Kaplan-Meier survival analysis demonstrated that 72%, 67%, 56%, and 48% of all patients remained asymptomatic at 1, 2, 3, and 4 years, respectively.Approximately 1 in 4 patients with FAI presents with symptoms in the contralateral hip, and an additional 1 in 4 patients develops significant symptoms in the following 4 years. Several factors, including low activity level, less hip rotational motion, and decreased head-neck offset ratio, were significantly associated with the development of symptoms, while the alpha angle and crossover sign were not.